When we're talking pressures using modern black powder and

>>34307892
Nope

>>34307961
Well then what can I use without paying fuckhuge money?

>>34308043

A gun barrel.

>>34308053
>schedule 80 pipe = $10
>a gun barrel = $100

Did you not read the other half of my post?

>>34308043
Something with some semblance of concentricity and material uniformity. Maybe a black powder barrel.

>>34308043
XXS heavy wall 1/2 or 3/4 would be the absolute min. for low power only loadings. Seamless hydraulic can be used but is also not considered safe.
Cheapest safe option is buyiing a barrel blank.

>>34308067
>holding a pipe bomb next to your face
>not holding a pipe bomb next to your face

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>>34308067
>$100 is "fuckhuge money"
You have to be 18 to post here.

>>34307892
>buy schedule 80 pipe
>build gun around it
>triple load it
>shoot it from behind a tree
>if it doesn't kB or deform you're probably OK

Find chunk of steel, Fold 1000 times like KATANAH, roll into tube, and you can shoot .500 S&W magnum out of it.

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>>34308067
"i want to build a functioning firearm, but i only want to use cardboard and string to save money"

Why not?

The 3D printed Liberator shoots 22lr out of a plastic barrel

>>34307892
Let me take a shower and then I'll get my computer. We'll do some napkin math to figure out what sort of garbage rod you can use to make a smoothbore ghetto blaster. From past experience looking into a similar concept for a cheap homemade 12ga shotty, the metal will run you about $12-$25/foot off the internet's (adjusted for shipping.)

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I mean, it comes down to how much pressure you're putting it through.

According to this website: http://www.engineeringtoolbox.com/wrought-steel-pipe-bursting-pressure-d_1123.html

1.5" Schedule 80 has a working pressure of 1,050 psi and a bursting pressure of 16,840 psi.

For reference:

As per SAAMI: http://saami.org/specifications_and_information/publications/download/Z299-2_ANSI-SAAMI_Shotshell.pdf#page=8

2-3/4" 12 gauge shells have a maximum average pressure of 11,500 psi and a maximum probable sample mean pressure of 12,800 psi.

If you use 3/4" Schedule 80 pipe, you're looking at a working pressure rating of 1,470 psi and a burst pressure of 11,730 psi. So anything stronger than a light target load would be a bad idea.

There are stronger pipe ratings that are more likely to work, but don't fuck with things you don't have a solid grasp on because it's easier to make a bomb than it is to make a gun.

>>34307892
given that you can shoot low brass smokeless out of black iron pipe, I'd say that you're fine as long as you proof test it

>>34308512
>>34307892
Alright, so here is some real quick and dirty math. Basically, the most important pressure inside a barrel is hoop stress or Von Mises Plane Stress. Given the dimensions and yield strength for a barrel made of a given material, you can roughly estimate the max allowable pressure. The equation is as follows:

P_allowed = (Sy / n) *((ro^2 - ri^2) / sqrt(3 * ro^4 + ri^4)) / 10^6

Where
Sy = Yield Strength in Pascals
n = factor of safety
ro = outer radius of barrel
ri = inner radius of barrel
P_allowed = maximum allowable pressure in MPa

For you barrel, I found some schedule 80 tube in 4130 steel here:
http://www.onlinemetals.com/merchant.cfm?id=250&step=2&top_cat=197

The yield strength of 4130 is about 460 MPa. Given your chosen barrel,
ro = 24.1mm (0.0241m)
ri = 19.1mm (0.0191m)
n = 1 (keep this in mind! we're in the danger zone)

This gives a P_allowed of 94 MPa, or about 13.6 ksi.

This, however, is misleading!

Continued later...

>>34308801
>Safety factor
If I might interject here...

SAAMI standards for definitive proof loads are to take the Maximum Probable Lot Mean (To use 2-3/4 12 gauge as an example again, 12,800 psi), multiply it by 1.55 and rounding up to the nearest multiple of 100 psi.
12,800 * 1.55 = 19,840 which, after rounding, gives a proof load of 19,900 psi. Far beyond the burst pressure of the schedule 80 pipe, but still below the burst pressure of the XXS pipe as per the website linked to above.

>>34308856
Also, that's just for the minimum proof. Maximum proof is a multiple of 1.7 and rounding down to the nearest multiple of 100 psi.

Using the same example, that'd be 12,800 * 1.7 = 21,760 --> 21,700 psi.

>>34308067
http://www.e-sarcoinc.com/45-rifled-barrel-blanks.aspx

Top of the list. Fuckn 38 seconds with google.
45 cal barrel blank. $28.

Your not good at this. Try a hobby with no sharp edges kid.

>>34307892
Not at all.

The pipe will bulge and probably explode pretty soon.

Get a lathe and 4140 then heat treat it . or buy a barrel blank.

Or chose a cheaper hobby.

File: 4130 fatigue curve.png (139KB, 676x473px) Image search: [Google]

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>>34308801
Cont.

Alright, so we have guesstimated how much pressure the barrel can survive before exploding. Great. How many cycles will it survive, though? For this, we can calculate the Von Mises Plane stress as follows:

sigma_e = n *Pi * sqrt((3 * ro^4 + ri^4) / (ro^2 - ri^2)^2) / 10^6

Where
Pi = max internal pressure in Pa
and sigma_e = Von Mises Plane Stress in MPa

Using 94 MPa as our Pi, a factor of safety of 1.5, and the same variables for barrel geometry, we get

sigma_e = 690 MPa

Looking at a fatigue diagram for 4130 steel, we can see that we get about 400 shots with this barrel before it blows up. Not great.

I have to ask, why are you going with such a fuckhuge bore of 1.5"? For my 12ga shotgun, I was looking into using two pipes: 0.76"x1" pipe for the barrel slid into a 1"x1.5" barrel to make a reinforced chamber (self-headspacing too--you just press the barrel into the chamber with a 12ga snap cap in the chamber until it is tight and then weld the barrel to the chamber. The shell rim indexes the round.)

Doing this allowed the shotgun to take up to 3" shells which run at about 132 MPa (19 ksi), resulting in a Von Mises Stress of 490 MPa with a factor of safety of 1.5. This means the barrel will survive up to 20,000 shots (assuming the rest of the gun can take it--that is a big "if").

Please keep in mind these calculations are very rough, and although I tried to build in as much safety as I could sometimes shit just goes wrong. Be safe and have fun learning shit as you research this project!

>>34308856
>>34308870
Yes, I totally agree that this pipe would not be safe by any means. I hope I addressed the issue that the lack of factor of safety gives misleading results if you don't look carefully in my second post.

I was also unaware that for firearms, minimum factor of safety is 1.55--1.7 should probably be a starting point now that you guys bring this up! I've been taking this project slow and am still in the concept stages until I can save enough money to buy some equipment. I will definitely take you advice to heart.

Nigger, Walmart regularly has CVA Wolf black powder rifles on clearance for like, $60 bucks at the end of hunting season. They're good rifles and won't blow your hands off.

>>34308964
Honestly, I'd suggest going beyond that, even. Build it to survive 1.8+ and it'll outlive you.

>>34308938
1.5" bore would make sense if he was making a mortar or something.

>>34308938
>>34308904
>>34308870

Taking into account a factor of safety of 1.7, we get a potential barrel life of 3,000 shots. Not great. I should look more into 4140 and heat treating like >>34308904 said.

>>34309002
You can get heavywalled 4140 pipes, a metal supplier might be able to get you a 5/8 pipe with 1/4 or less hole.

That's fine for a good number of calibers if you drill/ream that out. Up to 380 auto should be fine without further chamber support.

>>34308938
>>34308801
So since there's an engi here mind running numbers on a completely different thing?
6" 316L stainless schedule 10 cylinder with two hemispherical end caps. Expected max pressure of 400 psi and running pressure of ~250.
My back of envelope math says I should have more than enough safety margin but I had not even thought about how many pressure cycles it could take.

>>34309041
Thanks, I will take that into account. The project was originally based on the concept of making a single-shot bolt action shotgun that I could make with a hand drill, angle grinder, stick welder, dremel, and various hand tools. I eventually realized I am not good enough with hand tools to pull off, and so I practice and save money for a mill and lathe.
>>34309065
I only whipped those posts so quickly since I had already built a matlab program to run the calculations for me, hahaha. Are the endcaps also 0.049" thick like the pipe walls or are they reinforced to the point we can assume the pipe itself is probably the only failure mode?

>>34309103
0.134", same as the pipe thickness
Overall outside diameter of 6.625"
Been close to 15 years since I did anything with MatLab. Even then it was all statistical work and genetic probabililties.

>>34309103
For shotguns, doubled galvanized pipes work fine.

Another thing you can do to add chamber support is to thread on an end cap with the rear removed.

I know a guy who's trying to make a semi auto blow forward 12 gauge Shotgun out of home depot parts.

It's something I designed and I don't really know if it would work, but he's building it.

The Washbear uses only thin steel liners in a plastic cylinder.
It seems to be working alright.

Also, look at all revolvers, or hell, the weird pepperboxes and shit from the 1600's. They are thin as fuck.
Why do you think steel pipes are suddenly not good enough?

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>>34309103
>>34309065
I went ahead and ran the calculations for the tube , assuming that the endcaps were not something to worry about--I need to get to bed soon haha. Keep in mind, these calculations make a lot of assumptions (such as assuming pressure is experienced equally by the steel) and do not take into account localized pressure spikes due to how the pressure is introduced to the pressure chamber.

Alright, so 316L steel has a yield strength Sy of 170 MPa. Given schedule 10 pipe dimensions, converting 400 psi to metric to get 2.8 MPa, and taking a factor of safety of 1.7, we get your Von Mises in the pipe wall to be 21 MPa. This is far below your fatigue limit for 316L of 350 MPa, and as such the steel will be able to withstand these pressures for quite a while. The safety margin is wide enough that even running your vessel at elevated temperatures I think you should be ok as long as you take into account potential failures induced by manufacturing methods. I would also think that the caps should be fine too, but please look into it a bit more before pushing "go". Good luck!

>>34308043
Go find a pipe rated for 40 kpsi. That will give you a half-decent safety margin.

>>34309225
Thanks. That's what I was figuring, large enough safety margins can cover a multitude of sins.
Just need to get the material and start welding. Will also need to figure out a wand valve.

Don't do it OP, >>34308801 >>34308938 is trying to kill you, that makes mustard gas

>>34308938
What engineers get out of this type of stuff I will never understand. Do you pop a boner when someone asks you about the tensile strength of reinforced concrete? I understand everyone has their own specialties and fields of work but man do I just completely fail to understand the gratification engineers get from their work.

>>34309657
I'm genuinely curious what the fuck you're on about.

I cant speak for all engineers, but as someone studying Electrical/computer Engineering, its not about spouting random bullshit facts like "tensile strength of reinforced concrete", its about the end game. The product.

Which in this case is a gun. One you know is safe.

>>34309657
As someone a few years into a career in aerospace engineering, it's not the math that I get hard over. It's the airplanes coming out the other end of the factory and taking off.

I'll admit a drawing with good GD&T or a well written structural analysis do get my nips over 50 Rockwell C, though.

Sage for off-topic.